Post-menopausal hormone use is becoming increasingly widespread based on evidence of the benefits of estrogen use for bone and the heart. However, because estrogen alone substantially increases the risk of endometrial cancer, estrogen users who have not undergone a hysterectomy are frequently also placed on a progestogen (E/P), a strategy that reduces the likelihood of endometrial cancer when compared with use of estrogen alone. Unfortunately, there are almost no data on the risk of cardiovascular disease in post-menopausal women who use E/P combinations. In this case-control study, we seek to fill this knowledge gap. The primary aims are to estimate the relative risks of acute myocardial infarction (MI) and of stroke in users of E/P combinations 50-79 years of age. Secondarily, it aims to estimate the relative risks of MI and of stroke in users of estrogen alone. Cases (N = 815 for MI; N = 1167 for stroke) are women 50-79 hospitalized with MI or stroke in any of nine participating Northern California Kaiser Permanente hospitals in a 36 month period. For each case, one control, matched by year of birth, will be selected at random from among members of the Kaiser Permanente Health Plan age 50-79 years who can be expected to use the same nine hospitals for their medical care. Information about use of estrogen, E/P combinations, past use of oral contraceptives, menopause, hysterectomy and oophorectomy, demographics, general health status, preventive health care, and cardiovascular risk factors will be collected in interviews done of the subjects or, for fatal cases, a surrogate. Information about current use of estrogen and E/P combinations will also be gathered by reviewing medical records. Analysis will use conditional logistic regression to estimate the relative risks of MI and of stroke in users of E/P combinations, taking into account prior oophorectomy and other potential confounders. We will also estimate the risks of acute MI and of stroke in users of estrogen alone, accounting for prior oophorectomy and potential confounders.